Encoder wheels are used in speed sensor devices to determine the rotational speed of a component. For example, in motor vehicle applications, an encoder wheel often forms part of an anti-lock braking system for determining the rotational speed of the wheels. Other applications include coupling to engine crankshafts and within transmissions.
The encoder wheel typically includes an outer surface having magnetized ferrite therein. The ferrite is magnetized to form alternating north and south poles around the circumference of the encoder wheel. As the encoder wheel rotates, a magnetic sensor measures the change in the magnetic field of the alternating poles. From this alternating magnetic field, the rotational speed of the encoder wheel may then be calculated, and in turn the rotational speed of the component to which the encoder wheel is coupled is known. Alternatively, hall effect sensors, which do not use magnets, can also be utilized for detecting the rotational speed.
A conventional encoder wheel is produced from a tube of stamped steel with a ferrite loaded rubber compression molded thereon. However, in order to retain the ferrite loaded rubber, the stamped steel must have flanges or features to engage the rubber. This in turn enlarges the size of the encoder wheel. Moreover, such features increase the cost of manufacturing the encoder wheel and increase the costs of packaging. Finally, each encoder wheel is made separately and individually. This can lead to non-uniformity between encoders. Accordingly, it is an object of the present invention to provide an encoder wheel and method of making that addresses these limitations.